Portable terminals such as smartphones, tablet personal computers, and laptop personal computers are prevalently used. The portable terminal has a flat-panel display device in which a liquid crystal or an organic EL element, etc., is used. The display device is connected to a host device which outputs pixel data or commands, etc., and comprises a display panel, and a driver which processes the command and drives the display panel.
In the display device, pixels which are two-dimensionally arranged on a display panel comprise a common electrode and a pixel electrode, and the liquid crystal or the organic EL element is disposed between the common electrode and the pixel electrode. When the driver writes a pixel signal to the pixel of the display panel, the liquid crystal or the organic EL element between the common electrode and the pixel electrode is controlled, and an image is displayed.
Meanwhile, a display device which detects approach or contact of an input object such as a finger or a touch pen (also referred to as a stylus pen) on a screen has been widely used. An operation of causing the input object to approach or contact the screen is referred to as a touch operation or a touch, and position detection of the input object is referred to as touch detection. A touch detection method includes various types of methods such as optical, resistance, capacitive, and electromagnetic induction methods. The capacitive method corresponds to a detection method which uses occurrence of a change of an electrostatic capacitance between a pair of electrodes (referred to as a drive electrode and a detection electrode) by approach or contact of an input object, and has an advantage of having a relatively simple structure, and having small power consumption.
In the display device having the aforementioned touch detection function, as the capacitive-type detection method, a method of performing the detection by using occurrence of a change of an earth capacitance of the detection electrode by approach or contact of an object, more specifically, a method known as self capacitive sensing, is employed. In the self capacitive sensing, the drive electrode also serves as the detection electrode which detects approach or contact of the object.
For example, when a plurality of drive electrodes extend along a longitudinal direction of the display panel, and are arranged in parallel along a lateral direction, a select circuit which selects a video signal line, a self-capacitance detection line, and a driver chip which supplies a signal to the video signal line are arranged in this order a/t a lower area in the longitudinal direction of a peripheral area surrounding a display area.
In the arrangement as described above, the self-capacitance detection line is formed to extend along the lateral direction, while a connection line which supplies a signal to the video signal line is formed to extend along the longitudinal direction. Accordingly, the self-capacitance detection line and the connection line which supplies the signal to the video signal line cross each other, and a parasitic capacitance produced by this crossover constitutes a load at a driving operation by the self capacitive sensing. In particular, a load of the parasitic capacitance more greatly impacts detection in the self capacitive sensing than in mutual capacitive sensing.